Load control device for use with lighting circuits having three-way switches

ABSTRACT

A smart dimmer for control of a lighting load from an AC power source can replace any switch in a three-way or four-way lighting control system. The smart dimmer can be connected on the line-side or the load-side of a three-way system with a standard three-way switch in the other location. According to one embodiment of the present invention, the dimmer includes two triacs to control the intensity of the connected lighting load. The dimmer preferably includes two gate drive circuits coupled to the gates of the triacs for rendering the triacs conductive each half-cycle of the AC power source. The gate drive circuits include sensing circuits for detect whether the gates currents are flowing after the triacs are rendered conductive. A controller is operable to determine the state of the lighting load in response to whether the gate current is flowing or not flowing.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of commonly-assigned co-pending U.S. patent application Ser. No. 11/767,279, filed Jun. 22, 2007, entitled LOAD CONTROL DEVICE FOR USE WITH LIGHTING CIRCUITS HAVING THREE-WAY SWITCHES, which is a continuation-in-part of commonly-assigned co-pending U.S. patent application Ser. No. 11/447,496, filed Jun. 6, 2006, entitled DIMMER SWITCH FOR USE WITH LIGHTING CIRCUITS HAVING THREE-WAY SWITCHES, which claims priority from commonly-assigned U.S. Provisional Application Ser. No. 60/687,690, filed Jun. 6, 2005, entitled INTELLIGENT THREE-WAY AND FOUR-WAY DIMMERS. The entire disclosures of all applications are hereby incorporated by reference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to load control devices for electrical wiring systems having three-way switches. In particular, the present invention relates to a dimmer switch that can be substituted for a four-way switch, a line-side three-way switch, or a load-side three-way switch in lighting circuits having either two or more points of control, such as, for example, a four-way system.

2. Description of the Related Art

Three-way and four-way switch systems for use in controlling loads in buildings, such as lighting loads, are known in the art. Typically, the switches used in these systems are wired to the building's alternating-current (AC) wiring system, are subjected to AC source voltage, and carry full load current, as opposed to low-voltage switch systems that operate at low voltage and low current, and communicate digital commands (usually low-voltage logic levels) to a remote controller that controls the level of AC power delivered to the load in response to the commands. Thus, as used herein, the terms “three-way switch”, “three-way system”, “four-way switch”, and “four-way system” mean such switches and systems that are subjected to the AC source voltage and carry the full load current.

A three-way switch derives its name from the fact that it has three terminals and is more commonly known as a single-pole double-throw (SPDT) switch, but will be referred to herein as a “three-way switch”. Note that in some countries a three-way switch as described above is known as a “two-way switch”.

A four-way switch is a double-pole double-throw (DPDT) switch that is wired internally for polarity-reversal applications. A four-way switch is commonly called an intermediate switch, but will be referred to herein as a “four-way switch”.

In a typical, prior art three-way switch system, two three-way switches control a single load, and each switch is fully operable to independently control the load, irrespective of the status of the other switch. In such a system, one three-way switch must be wired at the AC source side of the system (sometimes called “line side”), and the other three-way switch must be wired at the load side of the system.

FIG. 1A shows a standard three-way switch system 100, which includes two three-way switches 102, 104. The switches 102, 104 are connected between an AC voltage source 106 and a lighting load 108. The three-way switches 102, 104 each include “movable” (or common) contacts, which are electrically connected to the AC voltage source 106 and the lighting load 108, respectively. The three-way switches 102, 104 also each include two fixed contacts. When the movable contacts are making contact with the upper fixed contacts, the three-way switches 102, 104 are in position A in FIG. 1A. When the movable contacts are making contact with the lower fixed contact, the three-way switches 102, 104 are in position B. When the three-way switches 102, 104 are both in position A (or both in position B), the circuit of system 100 is complete and the lighting load 108 is energized. When switch 102 is in position A and switch 104 is in position B (or vice versa), the circuit is not complete and the lighting load 108 is not energized.

Three-way dimmer switches that replace three-way switches are known in the art. An example of a three-way dimmer switch system 150, including one prior art three-way dimmer switch 152 and one three-way switch 104 is shown in FIG. 1B. The three-way dimmer switch 152 includes a dimmer circuit 152A and a three-way switch 152B. A typical, AC phase-control dimmer circuit 152A regulates the amount of energy supplied to the lighting load 108 by conducting for some portion of each half-cycle of the AC waveform, and not conducting for the remainder of the half-cycle. Because the dimmer circuit 152A is in series with the lighting load 108, the longer the dimmer circuit conducts, the more energy will be delivered to the lighting load 108. Where the lighting load 108 is a lamp, the more energy that is delivered to the lighting load 108, the greater the light intensity level of the lamp. In a typical dimming operation, a user may adjust a control to set the light intensity level of the lamp to a desired light intensity level. The portion of each half-cycle for which the dimmer conducts is based on the selected light intensity level. The user is able to dim and toggle the lighting load 108 from the three-way dimmer switch 152 and is only able to toggle the lighting load from the three-way switch 104. Since two dimmer circuits cannot be wired in series, the three-way dimmer switch system 150 can only include one three-way dimmer switch 152, which can be located on either the line side or the load side of the system.

A four-way switch system is required when there are more than two switch locations from which to control the load. For example, a four-way system requires two three-way switches and one four-way switch, wired in well known fashion, so as to render each switch fully operable to independently control the load irrespective of the status of any other switches in the system. In the four-way system, the four-way switch is required to be wired between the two three-way switches in order for all switches to operate independently, i.e., one three-way switch must be wired at the AC source side of the system, the other three-way switch must be wired at the load side of the system, and the four-way switch must be electrically situated between the two three-way switches.

FIG. 1C shows a prior art four-way switching system 180. The system 180 includes two three-way switches 102, 104 and a four-way switch 185. The four-way switch 185 has two states. In the first state, node A1 is connected to node A2 and node B1 is connected to node B2. When the four-way switch 185 is toggled, the switch changes to the second state in which the paths are now crossed (i.e., node A1 is connected to node B2 and node B1 is connected to node A2). Note that a four-way switch can function as a three-way switch if one terminal is simply not connected.

FIG. 1D shows another prior art switching system 190 containing a plurality of four-way switches 185. As shown, any number of four-way switches can be included between the three-way switches 102, 104 to enable multiple location control of the lighting load 108.

Multiple location dimming systems employing a smart dimmer switch and a specially designed remote (or “accessory”) switch that permit the dimming level to be adjusted from multiple locations have been developed. A smart dimmer is one that includes a microcontroller or other processing means for providing an advanced set of control features and feedback options to the end user. For example, the advanced features of a smart dimmer may include a protected or locked lighting preset, fading, and double-tap to full intensity. To power the microcontroller, smart dimmers include power supplies, which draw a small amount of current through the lighting load each half-cycle when the semiconductor switch is non-conducting. The power supply typically uses this small amount of current to charge a storage capacitor and develop a direct-current (DC) voltage to power the microcontroller. An example of a multiple location lighting control system, including a wall-mountable smart dimmer switch and wall-mountable remote switches for wiring at all locations of a multiple location dimming system, is disclosed in commonly assigned U.S. Pat. No. 5,248,919, issued on Sep. 28, 1993, entitled LIGHTING CONTROL DEVICE, which is herein incorporated by reference in its entirety.

Referring again to the system 150 of FIG. 1B, since no load current flows through the dimmer circuit 152A of the three-way dimmer switch 152 when the circuit between the supply 106 and the lighting load 108 is broken by either three-way switch 152B or 104, the dimmer switch 152 is not able to include a power supply and a microcontroller. Thus, the dimmer switch 152 is not able to provide the advanced set of features of a smart dimmer to the end user.

FIG. 2 shows an example multiple location lighting control system 200 including one wall-mountable smart dimmer switch 202 and one wall-mountable remote switch 204. The dimmer switch 202 has a Hot (H) terminal for receipt of an AC source voltage provided by an AC power supply 206, and a Dimmed Hot (DH) terminal for providing a dimmed-hot (or phase-controlled) voltage to a lighting load 208. The remote switch 204 is connected in series with the DH terminal of the dimmer switch 202 and the lighting load 208, and passes the dimmed-hot voltage through to the lighting load 208.

The dimmer switch 202 and the remote switch 204 both have actuators to allow for raising, lowering, and toggling on/off the light intensity level of the lighting load 208. The dimmer switch 202 is responsive to actuation of any of these actuators to alter the dimming level (or power the lighting load 208 on/off) accordingly. In particular, actuation of an actuator at the remote switch 204 causes an AC control signal, or partially rectified AC control signal, to be communicated from that remote switch 204 to the dimmer switch 202 over the wiring between the Accessory Dimmer (AD) terminal of the remote switch 204 and the AD terminal of the dimmer switch 202. The dimmer switch 202 is responsive to receipt of the control signal to alter the dimming level or toggle the load 208 on/off. Thus, the load can be fully controlled from the remote switch 204.

The user interface of the dimmer switch 202 of the multiple location lighting control system 200 is shown in FIG. 3. As shown, the dimmer switch 202 may include a faceplate 310, a bezel 312, an intensity selection actuator 314 for selecting a desired level of light intensity of a lighting load 208 controlled by the dimmer switch 202, and a control switch actuator 316. The faceplate 310 need not be limited to any specific form, and is preferably of a type adapted to be mounted to a conventional wall-box commonly used in the installation of lighting control devices. Likewise, the bezel 312 and the actuators 314, 316 are not limited to any specific form, and may be of any suitable design that permits manual actuation by a user.

An actuation of the upper portion 314A of the actuator 314 increases or raises the light intensity of the lighting load 208, while an actuation of the lower portion 314B of the actuator 314 decreases or lowers the light intensity. The actuator 314 may control a rocker switch, two separate push switches, or the like. The actuator 316 may control a push switch, though the actuator 316 may be a touch-sensitive membrane. The actuators 314, 316 may be linked to the corresponding switches in any convenient manner. The switches controlled by actuators 314, 316 may be directly wired into the control circuitry to be described below, or may be linked by an extended wired link, infrared (IR) link, radio frequency (RF) link, power line carrier (PLC) link, or otherwise to the control circuitry.

The dimmer switch 202 may also include an intensity level indicator in the form of a plurality of light sources 318, such as light-emitting diodes (LEDs). Light sources 318 may be arranged in an array (such as a linear array as shown) representative of a range of light intensity levels of the lighting load 208 being controlled. The intensity levels of the lighting load 208 may range from a minimum intensity level, which is preferably the lowest visible intensity, but which may be “full off”, or zero, to a maximum intensity level, which is typically “full on”, or substantially 100%. Light intensity level is typically expressed as a percent of full intensity. Thus, when the lighting load 208 is on, light intensity level may range from 1% to substantially 100%.

A simplified block diagram of the dimmer switch 202 and the remote switch 204 of the multiple location lighting control system 200 is shown in FIG. 4. The dimmer switch 202 employs a semiconductor switch 420 coupled between the hot terminal H and the dimmed hot terminal DH, to control the current through, and thus the light intensity of, the lighting load 208. The semiconductor switch 420 may be implemented as a triac or two field effect transistors (FETs) in anti-series connection. The semiconductor switch 420 has a control input (or gate), which is connected to a gate drive circuit 424. The input to the gate will render the semiconductor switch 420 conductive or non-conductive, which in turn controls the power supplied to the lighting load 208. The gate drive circuit 424 provides control inputs to the semiconductor switch 420 in response to command signals from a microcontroller 426.

The microcontroller 426 generates command signals to a visual display, e.g., a plurality of LEDs 418, for feedback to the user of the dimmer switch 202. The microcontroller 426 receives inputs from a zero-crossing detector 430 and a signal detector 432. A power supply 428 generates a DC output voltage V_(CC) to power the microcontroller 426. The power supply is coupled between the hot terminal H and the dimmed hot terminal DH.

The zero-crossing detector 430 determines the zero-crossings of the input AC waveform from the AC power supply 206. A zero-crossing is defined as the time at which the AC supply voltage transitions from positive to negative polarity, or from negative to positive polarity, at the beginning of each half-cycle. The zero-crossing information is provided as an input to microcontroller 426. The microcontroller 426 provides the gate control signals to operate the semiconductor switch 420 to provide voltage from the AC power supply 206 to the lighting load 208 at predetermined times relative to the zero-crossing points of the AC waveform.

Generally, two techniques are used for controlling the power supplied to the lighting load 208: forward phase control dimming and reverse phase control dimming. In forward phase control dimming, the semiconductor switch 420 is turned on at some point within each AC line voltage half-cycle and remains on until the next voltage zero-crossing. Forward phase control dimming is often used to control energy to a resistive or inductive load, which may include, for example, a magnetic low-voltage transformer or an incandescent lamp. In reverse phase control dimming, the semiconductor switch 420 is turned on at the zero-crossing of the AC line voltage and turned off at some point within each half-cycle of the AC line voltage. Reverse phase control is often used to control energy to a capacitive load, which may include, for example, an electronic low-voltage transformer. Since the semiconductor switch 420 must be conductive at the beginning of the half-cycle, and be able to be turned off with in the half-cycle, reverse phase control dimming requires that the dimmer have two FETs in anti-serial connection, or the like.

The signal detector 432 has an input 440 for receiving switch closure signals from momentary switches T, R, and L. Switch T corresponds to a toggle switch controlled by the switch actuator 316, and switches R and L correspond to the raise and lower switches controlled by the upper portion 314A and the lower portion 314B, respectively, of the intensity selection actuator 314.

Closure of switch T will connect the input of the signal detector 432 to the DH terminal of the dimmer switch 202, and will allow both positive and negative half-cycles of the AC current to flow through the signal detector. Closure of switches R and L will also connect the input of the signal detector 432 to the DH terminal. However, when switch R is closed, current can only flow through the signal detector 432 during the positive half-cycle of the AC power supply 406 because of a diode 434. In similar manner, when switch L is closed, current can only flow through the signal detector 432 during the negative half-cycles because of a diode 436. The signal detector 432 detects when the switches T, R, and L are closed, and provides two separate output signals representative of the state of the switches as inputs to the microcontroller 426. A signal on the first output of the signal detector 432 indicates a closure of switch R and a signal on the second output indicates a closure of switch L. Simultaneous signals on both outputs represents a closure of switch T. The microprocessor controller 426 determines the duration of closure in response to inputs from the signal detector 432.

The remote switch 204 provides a means for controlling the dimmer switch 202 from a remote location in a separate wall box. The remote switch 204 includes a further set of momentary switches T′, R′, and L′ and diodes 434′ and 436′. A wire connection is made between the AD terminal of the remote switch 204 and the AD terminal of the dimmer switch 202 to allow for the communication of actuator presses at the remote switch. The AD terminal is connected to the input 440 of the signal detector 432. The action of switches T′, R′, and L′ in the remote switch 204 corresponds to the action of switches T, R, and L in the dimmer switch 202.

The system shown in FIGS. 2, 3, and 4 provides a fully functional three-way switching system wherein the user is able to access all functions, such as, for example, dimming at both locations. However, in order to provide this functionality, both switching devices need to be replaced with the respective devices 202, 204.

Sometimes it is desired to place only one smart switch in the three-way or four-way switching circuit. As shown in FIG. 1B, it is not possible heretofore to do this by simply replacing the dimmer 152 with a smart dimmer, leaving mechanical three-way switch 104 in the circuit because when switch 104 breaks the circuit, power no longer is provided to the microcontroller of the smart dimmer (in place of the dimmer 152) because current no longer flows through the dimmer to the lighting load 108. The three-way and four-way dimmer switch according to the present invention provides a solution to this problem and also optionally provides a means for remote control of the switch.

In one prior art remote control lighting control system, a single multi-location dimmer and up to nine “accessory” dimmers can be installed on the same circuit to enable dimming from a plurality of controls. In the prior art, accessory dimmers are necessary because prior art multi-location dimmers are incompatible with mechanical three-way switches. Accessory dimmers installed throughout a house can greatly increase the cost of the components and of the installation of a dimming system.

Moreover, even though the multiple location lighting control system 200 allows for the use of a smart dimmer switch in a three-way system, it is necessary for the customer to purchase the remote switch 204 along with the smart dimmer switch 202. Often, the typical customer is unaware that a remote switch is required when buying a smart dimmer switch for a three-way or four-way system until after the time of purchase when the smart dimmer switch is installed and it is discovered that the smart dimmer switch will not work properly with the existing mechanical three-way or four-way switch. Therefore, there exists a need for a smart dimmer that may be installed in any location of a three-way or four-way system without the need to purchase and install a special remote switch.

A smart three-way switch has also been designed that operates with a conventional mechanical three-way switch, but that system requires rewiring of the mechanical three-way switch in order to provide proper three-way operation from both locations. This is the subject of commonly assigned U.S. patent application Ser. No. 11/125,045, filed May 9, 2005, entitled DIMMER FOR USE WITH A THREE-WAY SWITCH, which is incorporated herein by reference in its entirety.

SUMMARY OF THE INVENTION

The present invention provides a load control device adapted to be coupled to a circuit including an AC power source, a load, and a single-pole double-throw three-way switch. The load control device comprises: first, second, and third electrical load terminals, first and second controllably conductive devices, and a controller. The first and second controllably conductive devices each have a conductive state and a non-conductive state. The first controllably conductive device is electrically coupled between the first load terminal and the second load terminal such that when the first controllably conductive device is in the conductive state and the load control device is coupled to the circuit, a load current is operable to flow between the first load terminal and the second load terminal. The second controllably conductive device is electrically coupled between the first load terminal and the third load terminal such that when the second controllably conductive device is in the conductive state and the load control device is coupled to the circuit, the load current is operable to flow between the first load terminal and the third load terminal. The first and second controllably conductive devices have first and second control inputs, respectively, and are operable to enter the conductive state in response to first and second gate currents conducted through the first and second control inputs. The controller is operable to control the first and second controllably conductive devices to control the load between an on state and an off state. The controller operable to drive the first controllably conductive device to change the first controllably conductive device from the non-conductive state to the conductive state each half-cycle of the AC line voltage. The controller is operable to determine, in response to the magnitude of the first gate current through the first control input of the first controllably conductive device, whether the first controllably conductive device is presently conducting current to the load.

The present invention further provides a method for controlling a load in a circuit comprising a power source, the load, a load control device, and a single-pole double-throw three-way switch. The method comprises the steps of: (1) providing first, second, and third electrical load terminals on the dimmer switch; (2) electrically coupling a first controllably conductive device between the first load terminal and the second load terminal, the first controllably conductive device having a conductive state and a non-conductive, the first controllably conductive device arranged such that when the first controllably conductive device is in the conductive state, a load current is operable to flow between the first load terminal and the second load terminal, the first controllably conductive device having a first control input; (3) conducting a first gate current through the first control input to cause the first controllably conductive device to enter the conductive state; (4) electrically coupling a second controllably conductive device between the first load terminal and the third load terminal, the second controllably conductive device having a conductive state and a non-conductive state, the second controllably conductive device arranged such that when the second controllably conductive device is in the conductive state, the load current is operable to flow between the first load terminal and the third load terminal, the second controllably conductive device having a second control input; (5) conducting a second gate current through the second control input to cause the second controllably conductive device to enter the conductive state; (6) monitoring the first and second gate currents; and (7) determining, in response to the step of monitoring the first and second gate currents, whether the respective controllably conductive device is presently conducting the current to the load.

In addition, the present invention provides a load control system for controlling the amount of power delivered to an electrical load from an AC power source generating an AC line voltage. The load control system comprises a single-pole double-throw (SPDT) three-way switch and a load control device. The SPDT switch comprises a first fixed contact, a second fixed contact, and a movable contact adapted to be coupled to either the power source or the load. The SPDT three-way switch has a first state in which the movable contact is contacting the first fixed contact and a second state in which the movable contact is contacting the second fixed contact. The load control device comprises a first load terminal adapted to be coupled to either the power source or the load to which the SPDT three-way switch is not coupled to, a second load terminal coupled to the first fixed contact of the SPDT three-way switch, and a third load terminal coupled to the second fixed contact of the SPDT three-way switch. The load control device also comprises first and second controllably conductive devices, each having conductive and non-conductive states. The first and second controllably conductive devices have respective first and second control inputs and are operable to enter the conductive state in response to first and second gate currents conducted through the first and second control inputs, respectively. The load control device further comprises a controller operable to control the first and second controllably conductive devices. When the SPDT three-way switch is in the first state, the controller is operable to control the first controllably conductive device such that a load current is operable to flow through the second load terminal when the first controllably conductive device is in the conductive state. When the SPDT three-way switch is in the second state, the controller is operable to control the first controllably conductive device such that the load current is operable to flow through the third load terminal when the controllably conductive device is in the conductive state. The controller is operable to determine, in response to the magnitude of the first gate current through the first control input of the first controllably conductive device, whether the first controllably conductive device is presently conducting current to the load, and to determine, in response to the magnitude of the second gate current through the second control input of the second controllably conductive device, whether the second controllably conductive device is presently conducting current to the load.

Other features and advantages of the present invention will become apparent from the following description of the invention that refers to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

For the purpose of illustrating the invention, there is shown in the drawings a form, which is presently preferred, it being understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown. The features and advantages of the present invention will become apparent from the following description of the invention that refers to the accompanying drawings, in which:

FIG. 1A shows a prior art three-way switch system, which includes two three-way switches;

FIG. 1B shows an example of a prior art three-way dimmer switch system including one prior art three-way dimmer switch and one three-way switch;

FIG. 1C shows a prior art four-way switching system;

FIG. 1D shows a prior art extended four-way switching system;

FIG. 2 is a simplified block diagram of a typical prior art multiple location lighting control system;

FIG. 3 shows the prior art user interface of the dimmer switch of the multiple location lighting control system of FIG. 2;

FIG. 4 is a simplified block diagram of the dimmer switch and the remote switch of the prior art multiple location lighting control system of FIG. 2;

FIG. 5A is a simplified block diagram of a three-way lighting control system including a smart three-way dimmer according to the present invention;

FIG. 5B shows a state diagram summarizing the operation of the lighting control system of FIG. 5A;

FIG. 5C is a perspective view of a user interface of the smart three-way dimmer of FIG. 5A;

FIG. 6A is a simplified block diagram of a three-way lighting control system including a second embodiment of a smart three-way dimmer according to the present invention;

FIG. 6B is a simplified schematic diagram of a first detect circuit of the dimmer of FIG. 6A;

FIG. 7A is a simplified block diagram of a three-way lighting control system including a third embodiment of a smart three-way dimmer according to the present invention;

FIG. 7B shows a simplified schematic diagram of a current detect circuit of the dimmer of FIG. 7A;

FIG. 8 is a simplified block diagram of a four-way lighting control system including a smart four-way dimmer according to a fourth embodiment of the present invention;

FIG. 9 shows a state diagram summarizing the operation of the lighting control system of FIG. 8;

FIG. 10 is a flowchart of a control loop of the controller of the smart four-way dimmer of FIG. 8 for determining the state of the dimmer;

FIG. 11 is a flowchart of the process of the button routine of the control loop of FIG. 10;

FIG. 12 is a flowchart of the process of the current detect routine of the control loop of FIG. 10;

FIG. 13 is a flowchart of the process of the triac state routine of the control loop of FIG. 10;

FIG. 14 is a flowchart of the startup process of the controller of the dimmer switch of FIG. 8;

FIG. 15A is a simplified block diagram of a three-way system that includes a smart switch according to a fifth embodiment of the present invention;

FIGS. 15B and 15C are simplified diagrams showing waveforms of the operation of the smart switch of FIG. 15A;

FIG. 15D is a simplified flowchart of a smart switch procedure executed by a controller of the smart switch of FIG. 15A;

FIG. 16A is a simplified block diagram of a three-way system that includes a smart switch according to a sixth embodiment of the present invention with the smart switch coupled to the line-side of the system;

FIG. 16B is a simplified schematic diagram showing current sense circuits and a line voltage detect circuit of the smart switch of FIG. 16A in greater detail;

FIG. 16C is a simplified block diagram of the three-way system of FIG. 16A with the smart switch coupled to the load-side of the system;

FIGS. 17A and 17B are simplified diagrams showing waveforms of the operation of the smart switch of FIG. 16A;

FIG. 18A is a simplified flowchart of a button procedure executed by a controller of the smart switch of FIG. 16A;

FIGS. 18B and 18C are simplified flowcharts of a zero-crossing procedure executed by the controller of the smart switch of FIG. 16A;

FIG. 18D is a simplified flowchart of an ON routine executed by the controller of the smart switch of FIG. 16A;

FIG. 18E is a simplified flowchart of an OFF routine executed by the controller of the smart switch of FIG. 16A;

FIG. 19 is a simplified block diagram of a three-way system 1900 that includes a smart dimmer according to a seventh embodiment of the present invention;

FIGS. 20A and 20B are simplified diagrams showing waveforms of the operation of the smart dimmer of FIG. 19; and

FIG. 21 is a simplified flowchart of a zero-crossing procedure executed by a controller of the smart dimmer of FIG. 19.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

The foregoing summary, as well as the following detailed description of the preferred embodiments, is better understood when read in conjunction with the appended drawings. For the purposes of illustrating the invention, there is shown in the drawings an embodiment that is presently preferred, in which like numerals represent similar parts throughout the several views of the drawings, it being understood, however, that the invention is not limited to the specific methods and instrumentalities disclosed.

FIG. 5A is a simplified block diagram of a three-way lighting control system 500 including a smart three-way dimmer switch 502 according to the present invention. The dimmer 502 and a standard three-way switch 504 are connected in series between an AC voltage source 506 and a lighting load 508. The dimmer 502 includes a hot terminal H that is coupled to the AC voltage source 506 and two dimmed hot terminals DH1, DH2 that are connected to the two fixed contacts of the three-way switch 504. The common terminal of the three-way switch 504 is coupled to the lighting load 508. Alternatively, the dimmer 502 could be connected on the load-side of the system 500 with the three-way switch 504 on the line-side. The dimmer 502 can be installed to replace an existing three-way switch without the need to replace the other existing three-way switch 504, and without the need for a wiring change to the three-way switch being replaced. The terminals H, DH1, DH2 of the dimmer 502 may be screw terminals, insulated wires or “flying leads”, stab-in terminals, or other suitable means of connecting the dimmer to the AC voltage source 506 and the lighting load 508.

In this embodiment of the smart two-wire dimmer switch 502, two bidirectional semiconductor switches 510, 514 are used. The semiconductor switches 510, 512 may comprise thyristors, such as triacs or silicon-controlled rectifiers (SCRs). Further, each semiconductor switch 510, 512 may comprise another type of semiconductor switching circuit, such as, for example, a FET in a full-wave rectifier bridge, two FETs in anti-series connection, or one or more insulated-gate bipolar junction transistors (IGBTs). As shown in FIG. 5A, each semiconductor switch 510, 512 is implemented as a triac. The first triac 510 has two main load terminals connected in series between the hot terminal H and the first dimmed hot terminal DH1. The first triac 510 has a gate (or control input) that is coupled to a first gate drive circuit 512. The second triac 514 has two main load terminals connected in series between the hot terminal H and the second dimmed hot terminal DH2 and has a gate that is coupled to a second gate drive circuit 516. The first and second triacs 510, 514 are rendered conductive in response to the conduction of gate currents through the respective gates of the triacs.

The dimmer 502 further includes a controller 518 that is coupled to the gate drive circuits 512, 516 to control the conduction times of the triacs 510, 514 each half-cycle. The controller 518 is preferably implemented as a microcontroller, but may be any suitable processing device, such as a programmable logic device (PLD), a microprocessor, or an application specific integrated circuit (ASIC). The controller 518 drives the triacs 510, 514 to render the triacs conductive for a portion of each half cycle of the AC voltage source 506. Accordingly, the controller 518 is operable as to control the intensity of the lighting load 508 using a standard forward phase-control technique, as is well-known to one of ordinary skill in the art.

As defined herein, “driving” refers to applying a control signal to a gate of a thyristor (such as a triac or an SCR) to enable a gate current to flow in the gate of the thyristor, such that the thyristor is conductive. When the thyristor is “conductive”, the gate current flows through the gate of the thyristor and the thyristor is operable to conduct a load current. The load current is defined as a current having a magnitude greater than the latching current of the thyristor. If the current through the main load terminals of the thyristor exceeds the latching current of the thyristor (while the thyristor is being driven), the thyristor then conducts the load current and the thyristor is defined to be in “conduction”.

A power supply 520 generates a DC voltage, V_(CC), to power the controller 518. The power supply 520 is coupled from the hot terminal H to the first dimmed hot terminal DH1 through a first diode 522 and to the second dimmed hot terminal DH2 through a second diode 524. This allows the power supply 520 to draw current through the first dimmed hot terminal DH1 when the three-way switch 504 is in position A and through the second dimmed hot terminal DH2 when the three-way switch 504 is in position B. The power supply 520 is able to charge when the triacs 510, 514 are both not conducting and there is a voltage potential developed across the dimmer 520.

The dimmer 502 further includes a zero-crossing detector 526 that is also coupled between the hot terminal H and the dimmed hot terminals DH1, DH2 through the diodes 522, 524, respectively. The zero-crossing detector 526 provides a control signal to the controller 518 that identifies the zero-crossings of the AC supply voltage. The controller 518 determines when to turn on the triacs 510, 514 each half-cycle by timing from each zero-crossing of the AC supply voltage.

A user interface 528 is coupled to the controller 518 and to allow a user to determine a desired lighting level (or state) of the lighting load 508. The user interface 528 provides a plurality of actuators for receiving inputs from a user. For example, the user interface 528 may comprise a toggle button 560 (i.e., a tap switch) and an intensity actuator 570 (i.e., a slider control) as shown in FIG. 5C. In response to an actuation of the toggle button 560, the controller 518 will toggle the state of the lighting load 508 (i.e., from on to off and vice versa) by changing which one of the two triacs 510, 514 is conducting. The controller 518 drives the triacs 510, 514 conduct on a complementary basis, such that only one of the two triacs operable to conduct the load current to the lighting load 508 at a single time. In this way, the dimmer 502 operates similarly to a standard SPDT switch by allowing current to either flow through the first dimmed hot terminal DH1 or the second dimmed hot terminal DH2 solely in response to an actuation of the toggle button 560. Alternatively, the user interface 528 may include a separate on button and off button, which will cause the lighting load 508 to turn on and off, respectively. Movement of the intensity actuator 570 will cause the dimmer 502 to control the intensity of the lighting load 508.

Further, the user interface 528 may comprise a visual display for providing feedback of the state of the lighting load 508 or the dimmer 502 to the user. The visual display may comprise, for example, a plurality of light-emitting diodes (LEDs), which may be selectively illuminated by the controller 518. A visual display is described in greater detail in previously-referenced U.S. Pat. No. 5,248,919.

The dimmer 502 further includes an airgap switch 530 for preventing current flowing through either of the triacs 510, 514, and an inductor 531 for providing electromagnetic interference (EMI) filtering.

When the three-way switch 504 is in position A and the desired state of the lighting load 508 is on, the controller 518 will turn the first triac 510 on for a portion of each half-cycle, while maintaining the second triac 514 in the non-conducting state. If the three-way switch 504 is then toggled from position A to position B, current will not flow to the lighting load 508 since the second triac 514 is not conducting. Therefore, the lighting load 508 will not be illuminated. Alternatively, if the three-way switch 504 is in position A, the lighting load 508 is on, and the toggle button 560 of the user interface 528 is actuated, the controller 518 will cause the first triac 510 to stop conducting and the second triac 514 to begin conducting. The lighting load 508 will be off because the controller 518 is driving the second triac 514 while the three-way switch 504 is in position A. If the toggle button 560 of the user interface 528 is actuated again, the controller 518 will stop driving the second triac 514 and will cause the first triac 510 to begin conducting, thus causing the lighting load 508 to illuminate again.

Similarly, when the three-way switch 504 is in position B and the desired state of the lighting load 508 is on, the controller 518 will turn the second triac 514 on for a portion of each half-cycle, while maintaining the first triac 510 in the non-conducting state. If the three-way switch 504 is then switched to position A, the current path to the lighting load 508 is interrupted and the lighting load will be off. Also, if the three-way switch 504 is in position B, the lighting load 508 is on, and the toggle button 560 of the user interface 528 is actuated, the controller 528 will cause the second triac 514 to stop conducting and the first triac 510 to begin conducting. The lighting load 508 will be off because the first triac 510 is conducting and the three-way switch 504 is in position B.

The power supply 520 preferably has a large enough storage capacitor to power the controller 518 during the times when the three-way switch 504 is transitioning from position A to position B and vice versa. For example, as the three-way switch 504 is toggled, current temporarily will not flow through either of the dimmed hot terminals DH1, DH2 as the movable contact transitions and the power supply 520 will provide power to the controller 518 by virtue of the internal storage capacitor. The amount of power that the power supply 520 needs to provide when the three-way switch 504 is transitioning is dependent on the transitioning time required for the movable contact to move from one fixed contact to the other.

However, it is not always possible to guarantee that the power supply 520 will be able to power the controller 518 and other low voltage circuitry during the time when the three-way switch 504 is transitioning between positions. Because of space limitations in a wall-mountable dimmer switch, it is not possible to simply include a particularly large storage capacitor in the power supply 520 to provide power during the transitioning time. Also, since the transitioning time is dependent on the force that a user exerts on the actuator of the three-way switch 504, the transitioning time can vary widely from one transition to the next. All three-way switches 504 include a region of “dead travel”, i.e., when the movable contact of the three-way switch is approximately half way between position A and position B and is not contacting either of the fixed contacts. Sometimes, it is possible for the three-way switch 504 to be sustained in the region of dead travel, such that no current may flow through the power supply 520 for an indeterminate period of time.

Accordingly, the dimmer 502 includes a memory 532 that enables the dimmer 502 to return to the appropriate state, i.e., to control the correct one of the two triacs 510, 514, if power to the dimmer 502 is temporarily lost when the three-way switch 504 is transitioning. The memory 532 is coupled to the controller 518. Whenever the toggle button 560 of the user interface 528 is actuated, the controller 518 stores in the memory 532, which one of the triacs 510, 514 is presently being controlled. In this way, if dimmer 502 temporarily loses power and the DC voltage V_(CC) falls below a level that allows for proper operation of the controller 518, the controller will read from the memory 532 which triac 510, 514 to control at “power up”, i.e. when the DC voltage V_(CC) rises back above the level that ensures proper operation of the controller.

FIG. 5B shows a state diagram 550 summarizing the operation of the lighting control system 500 of FIG. 5A. Two states 552, 554 are shown in which the lighting load 508 will be on since the three-way switch 504 is in the correct position to complete the circuit through the conducting triac. For example, at state 552, when the three-way switch 504 is in position A, the first triac 510 is able to conduct current to thus control the lighting load 508. The state diagram 550 also includes two states 556, 558 in which the lighting load 508 will be off since the three-way switch 504 is not in a position to conduct current through the triac that is enabled for conduction. A transition between states can be caused by one of three actions: a toggle of the three-way switch 504 from position A to position B (designated by ‘B’ in FIG. 5B), a toggle of the three-way switch 504 from position B to position A (designated by ‘A’), and an actuation of the toggle button 560 of the user interface 528 (designated by ‘T’).

FIG. 6A shows a simplified block diagram of a three-way lighting control system 600 including a second embodiment of a smart three-way dimmer switch 602 according to the present invention. A first detect circuit (or sensing circuit) 636 is coupled across the first triac 510 and a second detect circuit (or sensing circuit) 638 is coupled across the second triac 514. The detect circuits 636, 638 provide control signals to the controller 618 representative of electrical characteristics of the first dimmed hot terminal DH1 and the second dimmed hot terminal DH2, respectively. Each of the electrical characteristics may be a voltage developed across one of the respective triacs. Alternatively, the detect circuits 636, 638 may be placed in series with the dimmed hot terminals DH1, DH2 and the electrical characteristics may be currents through the dimmed hot terminals. In essence, the sensing of the electrical characteristics provides a determination of whether a path of continuity exists between hot and neutral of the AC voltage source 506 through the lighting load 508, the three-way switch 504, and the three-way dimmer switch 602, at either the first dimmed hot terminal DH1 or the second dimmed hot terminal DH2.

The controller 618 uses this information to determine the position of the three-way switch 504 in the system 600. For example, when the three-way switch 504 is in position A and the first triac 510 is non-conductive, a voltage will develop across the first detect circuit 636, which will output a signal indicating that the three-way switch 504 is in position A. Similarly, when the three-way switch 504 is in position B, the second detect circuit 638 will output a corresponding signal to the controller 618. The controller 618 uses the information of the state of the three-way switch 504 to provide feedback to the user via a plurality of LEDs on a user interface 628 and may provide feedback information to other control devices via an optional communication circuit 634. For example, the user interface 628 may be the same as the user interface shown in FIG. 3.

The communication circuit 634 may be coupled to a communications link, for example, a wired serial control link, a power-line carrier (PLC) communication link, or a wireless communication link, such as an infrared (IR) or a radio frequency (RF) communication link. An example of an RF lighting control system is described in commonly assigned U.S. Pat. No. 5,905,442, issued May 18, 1999, entitled METHOD AND APPARATUS FOR CONTROLLING AND DETERMINING THE STATUS OF ELECTRICAL DEVICES FROM REMOTE LOCATIONS, the entire disclosure of which is hereby incorporated by reference.

Instead of providing complementary control of the triacs 510, 514, the controller 618 could control the triacs to the same state at the same time. For example, when the first triac 510 is conducting and the second voltage detect circuit 638 determines that the three-way switch 504 has been toggled to position B, the controller could cause both triacs to stop conducting since the desired lighting level of the lighting load 508 is off. When neither triac 510, 514 is conducting, substantially no power, i.e., only an amount of power that will not illuminate the lighting load 508, is conducted to the lighting load.

Accordingly, the controller is operable to detect a change of the position of the three-way switch 504 and can determine when to toggle power to the load based on the three-way switch position change and the present state of the dimmer. Thus, the embodiments shown in FIGS. 5A and 6A are compatible with a mechanical three-way switch 504.

FIG. 6B is a simplified schematic diagram of a possible implementation of the first detect circuit 636. Since the voltage provided across the detect circuit 636 is an AC line voltage, the detect circuit includes an optocoupler 640. A resistor 642 is provided in series with the photodiodes 640A, 640B of the optocoupler 640 to limit the current through the photodiodes. The voltage at the collector of the phototransistor 640C of the optocoupler 640 is provided to the controller 618. A resistor 646 is provided in series with the phototransistor 640C to pull the voltage provided to the controller 618 up to the DC voltage V_(CC) of the power supply 520 when the phototransistor is not conducting (i.e., when there is no voltage across the detect circuit 636).

When a voltage is produced across the detect circuit 636, current flows through the photodiode 640A in the positive half-cycles and the photodiode 640B in the negative half-cycles. Hence, the phototransistor 640C conducts and the voltage at the collector of the phototransistor is pulled down to a circuit common 648. The schematic diagram of the second detect circuit 638 is identical to the schematic diagram of the first detect circuit 636 shown in FIG. 6B, differing only in the fact that the second detect circuit 638 is connected between the hot terminal H and the second dimmed hot terminal DH2. Alternatively, the first and second detect circuits 636, 638 could be implemented as a simple resistive circuit (not shown), for example, a resistor divider, with the controller 518 operable to detect a voltage produced by the resistive circuit.

FIG. 7A shows a simplified block diagram of a three-way lighting control system 700 including a third embodiment of a smart three-way dimmer switch 702 according to the present invention. In this embodiment, the dimmer switch 702 includes a single controllably conductive device, for example, a bidirectional semiconductor switch, such as a triac 710. A controller 714 is coupled to the gate of the triac 710 through a gate drive circuit 712 and controls the conduction time of the triac each half-cycle. A power supply 716 is coupled across the triac 710 and generates a DC voltage VCC to power the controller 714. A zero-crossing detector 718 determines the zero-crossing points of the AC voltage source 506 and provides this information to the controller 714. A user interface 720 provides inputs to the controller 714 from a plurality of buttons (including a toggle button) and includes a plurality of LEDs for feedback to a user. A communication circuit 722 allows the controller 714 to transmit and receive messages with other control devices. An airgap switch 724 disconnects the dimmer switch 702 and the lighting load 508 from the AC voltage source 506. An inductor 725 is in series with the triac 710 and provides EMI filtering. A memory 726 stores the present state of the dimmer switch 702, such that the controller 714 can properly operate the triac 710 at power up.

The dimmer 702 also includes a current detect circuit (sensing circuit) 728 that is coupled between the first dimmed hot terminal DH1 and the second dimmed hot terminal DH2. The current detect circuit 728 is operable to detect when there is current flowing through the second dimmed hot terminal DH2 and to accordingly provide a control signal to the controller 714. The power supply 716 provides a current path through the current detect circuit 728 when the triac 710 is non-conducting. When the three-way switch 504 is in position B, the charging current through the power supply 716 will flow through the second dimmed hot terminal DH2. The current detect circuit 728 will sense the charging current and indicate to the controller 714 that the three-way switch is in position B. When the three-way switch 504 is in position A, no current will flow through the current detect circuit 728 and no signal will be provided to the controller 714. Thus, the controller 714 is able to determine the state of the three-way switch 504 and to control the state of the lighting load 508 (i.e., on or off) accordingly.

The memory 726 stores the state of the triac 710 and of the three-way switch 504. If the power supply 716 is unable to supply power to the controller 714 through the duration of a transition of the three-way switch 504, the controller 714 will reset, i.e., power down and then power up when the three-way switch 504 has finished the transition. At power up, the controller 714 of the dimmer 702 checks the status of the three-way switch 504 from the control signal of the current detect circuit 728 and compares the present state of the three-way switch to the state of the three-way switch that is stored in the memory 726. If the status of the three-way switch 504 has changed, the controller 714 will toggle the state of the triac 710 based on the present state of the triac that is stored in the memory 726.

FIG. 7B shows a simplified schematic diagram of the current detect circuit (sensing circuit) 728 of the dimmer 702. The current detect circuit 728 includes a current sense transformer 730 that has a primary winding coupled in series between the dimmed hot terminals DH1, DH2. The current sense transformer 730 only operates above a minimum operating frequency, for example, 100 kHz, such that current only flows in the secondary winding when the current waveform through the primary winding has a frequency above the minimum operating frequency. The current sense transformer 730 detects the falling edge of the current waveform through the power supply 716 when the charging current flows through the second dimmed hot terminal DH2. Since the dimmer 702 is using a triac as the semiconductor switch, the dimmer operates using forward phase control dimming, in which the triac 710 is non-conductive at the beginning of each half-cycle. Thus, the power supply 716 charges at the beginning of each half-cycle. When the power supply 716 stops charging during a half-cycle, the charging current through the power supply will drop to zero. Since the falling time of the current waveform through the primary winding of the current sense transformer 730 is very short (i.e., the waveform has a high-frequency component), a current will flow in the secondary of the current sense transformer when the switch 504 is in position B. An example of the current sense transformer 730 is part number CT319-200, manufactured by Datatronic, Ltd.

The secondary winding of the current sense transformer 730 is coupled across a resistor 732. The resistor 732 is further coupled between circuit common and the negative input of a comparator 734. A reference voltage is produced by a voltage divider comprising two resistors 736, 738 and is provided to the positive input of the comparator 734. The output of the comparator 734 is tied to V_(CC) through a resistor 740 and is coupled to the controller 714. When current flows through the secondary winding of the current sense transformer 730, a voltage is produced across the resistor 732 that exceeds the reference voltage. The comparator 734 then drives the output low, signaling to the controller 714 that current has been sensed. Alternatively, the current detect circuit 728 may be implemented using an operational amplifier or a discrete circuit comprising one or more transistors rather than the comparator 734.

FIG. 8 is a simplified block diagram of a four-way lighting control system 800 including a smart four-way dimmer switch 802 according to a fourth embodiment of the present invention. The dimmer 802 and two three-way switches 803, 804 are coupled between an AC voltage source 806 and a lighting load 808. The dimmer 802 has replaced the four-way switch 185 in the four-way lighting control system 180 of FIG. 1C.

The dimmer 802 operates on the same principles as the dimmer 702 of FIG. 7A. However, the dimmer 802 includes an additional hot terminal H2 that is coupled to the three-way switch 803 on the line-side of the system 802. The dimmer 802 further comprises a second current detect circuit (sensing circuit) 829 that is coupled between the hot terminals H, H2 and provides a signal to a controller 814. The second current detect circuit 829 operates in the same manner as the first current detect circuit 728. When current is detected flowing through the second current detect circuit 829, the controller 814 determines that the line-side three-way switch 803 is in position D. When no current is flowing through the second current detect circuit 829, the three-way switch 803 is in position C. Thus, the controller 814 is able to determine the states of both the line-side three-way switch 803 and the load-side three-way switch 804 and to operate the triac 710 accordingly. When either three-way switch 803, 804 is toggled, or the toggle button of the user interface 720 is actuated, the controller 714 will toggle the state of the lighting load 808.

Even though the four-way dimmer switch 802 has four connections, the dimmer could be installed in a three-way system (in place of the three-way dimmer switch 502 in FIG. 5A or three-way dimmer switch 702 in FIG. 7A). One of the additional terminals DH2 or H2 would not be connected in the system 800. So, the dimmer 802 allows for a single device that can be installed in any location of a four-way or three-way system without the need to determine in advance what kind of switch the dimmer will be replacing.

FIG. 9 shows a state diagram 900 summarizing the operation of the lighting control system 800 of FIG. 8. In four states 902, 904, 906, 908, the triac 710 will be conducting since the desired state of the lighting load 808 is on. The state diagram 900 also shows four states 912, 914, 916, 918 in which the desired state of the lighting load 808 is off. A transition between states can be caused by one of five actions: a toggle of the three-way switch 804 from position A to position B (designated by ‘B’ in FIG. 6B), a toggle of the three-way switch 804 from position B to position A (designated by ‘A’), a toggle of the three-way switch 803 from position C to position D (designated by ‘D’), a toggle of the three-way switch 803 from position D to position C (designated by ‘C’), and an actuation of the toggle button of the user interface 720 (designated by ‘T’) (or when a “toggle” signal is received via the communication circuit 722). Note that in all states of the state diagram 900, the triac 710 is operable to conduct current to the lighting load 808 to control the state of the lighting load independent of the states of the three-way switches 803, 804.

The state diagram 900 thus identifies the status of the three-way switch 803, the three-way switch 804, and the triac 710 (and thus the lighting load 808) for all possible states and shows all the state transitions when the three-way switches 803, 804 are toggled and the toggle button of the user interface 720 is actuated (or when a “toggle” signal is received via the communication circuit 722).

FIG. 10 is a flowchart of a state control procedure 1000 of the controller 814 for determining the state of the dimmer 802. The state control procedure 1000 runs periodically, for example, approximately every 6 msec. The state control procedure 1000 includes a button routine 1100, a current detect routine 1200, and a triac state routine 1300. While the button routine 1100, the current detect routine 1200, and the triac state routine 1300 are shown executing in sequential order in FIG. 10, these routines alternatively could each be called from different pieces of software and each be executed at a different interval.

The controller 814 utilizes a FIFO (first in, first out) stack to store requests for the triac state routine 1300 to change the state of the triac 710. The button routine 1100 and the current detect routine 1200 are both operable to load an event (for example, a “toggle event”) into the FIFO stack. The triac state routine loads these events from the FIFO stack and processes the events. In the discussion of FIGS. 10 through 14, only toggle events are discussed. However, other events, such as “increase intensity” or “decrease intensity”, could be loaded into the FIFO stack by other routines (not described).

In the state control procedure 1000, the controller 814 utilizes three variables: TRIAC_STATUS, 1ST_DETECT, and 2ND_DETECT that are stored in the memory 726. The variable TRIAC_STATUS stores the conduction state of the triac 710, i.e., either ON or OFF. The variables 1ST_DETECT and 2ND_DETECT store the state of the first current detect circuit 728 and the second current detect circuit 829, respectively. The possible values for the variables 1ST_DETECT and 2ND_DETECT are TRUE (when current is detected) and FALSE (when current is not detected).

A flowchart describing the process of the button routine 1100 is shown in FIG. 11. At step 1110, the controller 814 first checks the toggle button of the user interface 720. If the toggle button is being pressed at step 1112, the controller 814 will load a “toggle event” into the FIFO stack at step 1114 and exit the process. If the toggle button is not being pressed at step 1112, the process simply exits.

FIG. 12 is a flowchart of the process of the current detect routine 1200. The outputs of the first current detect circuit 728 and second current detect circuit 829 are coupled to separate interrupt inputs on the controller 814. Whenever an input is provided from the first current detect circuit 728, a first interrupt routine is executed to set a first current detect flag. Similarly, whenever an input is provided from the first current detect circuit 728, a second interrupt routine is executed to set a second current detect flag.

Referring to FIG. 12, the first current detect flag is first checked at step 1210. At step 1212, if the first current detect flag has changed states, i.e., the new state of the first current detect circuit is not equal to the value stored in the variable 1ST_DETECT, the process moves to step 1214, where a determination is made as to whether the present value of the variable 1ST_DETECT is equal to TRUE. If so, the variable 1ST_DETECT is set to FALSE at step 1216. Otherwise, the variable 1ST_DETECT is set to TRUE at step 1218. Next, the controller 814 will load a “toggle event” into the FIFO stack at step 1220.

After loading a toggle event into the FIFO stack at step 1220, or after detecting no change of state of the first current detect circuit 728 at step 1212, the output of the second current detect circuit 829 is checked at step 1222. At step 1224, if the output of the second current detect circuit 829 has changed states, i.e., the new state of the second current detect circuit is not equal to the value stored in the variable 2ND_DETECT, a determination is made as to whether the present value of the variable 2ND_DETECT is equal to TRUE at step 1226. If so, the variable 2ND_DETECT is set to FALSE at step 1228; otherwise, the variable 2ND_DETECT is set to TRUE at step 1230. Next, the controller 714 will load a toggle event into the FIFO stack at step 1232 and exit.

At step 1224, if the output of the second current detect circuit 829 has not changed states, then the process simply exits without loading a toggle event into the FIFO stack.

FIG. 13 is a flowchart of the process of the triac state routine 1300. First, a toggle event is loaded from the FIFO stack (and deleted from the stack at the same time) at step 1310. If there is a toggle event in the FIFO stack to handle at step 1312, the triac state will be toggled. At step 1314, if the variable TRIAC_STATE is equal to OFF, then the variable TRIAC_STATE is set to ON at step 1316. Otherwise, the variable TRIAC_STATE is set to OFF at step 1318. At step 1320, the variables TRIAC_STATE, 1ST_DETECT, and 2ND_DETECT are stored in the memory 726. The process loops until there are no toggle events to handle at step 1312, at which time the process exits.

FIG. 14 is a flowchart of the startup process 1400 that the controller 814 performs at power up, for example, if the controller 814 loses power while a connected three-way or four-way switch is transitioning. First, the controller 814 reads the variables TRIAC_STATE, 1ST_DETECT, and 2ND_DETECT from the memory 726 at step 1410. Next, the controller 814 checks the status of the first current detect circuit 728 and the second current detect circuit 829 in the current detect routine 1100. Next, the controller 814 determines whether to change the variable TRIAC_STATE in the triac state routine 1200. Finally, the process exits to begin normal operation executing the state control procedure 1000 of FIG. 10.

Although the embodiment of FIG. 8 shows two current detect circuits 728, 829. Additional sensing circuits could be employed. For example, a current detect circuit could be employed coupled in series with each terminal of the smart four-way dimmer switch 802 for a total of four current detect circuits.

The smart dimmers 502, 602, 702, and 802 preferably control incandescent and magnetic-low voltage loads using standard forward phase-control techniques. With such load types, the power supplies of the dimmers are able to draw a small amount of current through the loads without illuminating the loads. However, other load types, such as fluorescent loads, are susceptible to illuminating when even a small amount of current flows though the load. Since the dimmer topologies of FIG. 5A-FIG. 8 depend upon current flowing through the load in order to determine the state of a connected three-way or four-way switch, it is not preferable to use the smart dimmers 502, 602, 702, and 802 to control those load types that may illuminate due to a low amount of current flowing through the load. It is therefore desirable to provide an electronic three-way load control device, such as an electronic switch, which is able to control a wide variety of load types.

FIG. 15A is a simplified block diagram of a three-way system 1500 that includes a smart electronic switch 1502 according to a fifth embodiment of the present invention. The smart switch 1502 and a three-way switch 1504 are coupled between an AC voltage source 1506 and a lighting load 1508. The smart switch 1502 includes two semiconductor switches, e.g., two triacs 1510, 1514, coupled between the hot terminal and respective switched hot terminals SH1, SH2. A controller 1518 controls the triacs 1510, 1514 (via two gate drive circuits 1512, 1516) on a complementary basis, i.e., in a similar manner as the smart dimmer 502 of FIG. 5A. Accordingly, when the first triac 1510 is conductive, the second triac 1514 is non-conductive, and when the second triac 1514 is conductive, the first triac 1510 is non-conductive. The switch 1502 further includes an airgap switch 1530 for preventing current flowing through either of the triacs 1510, 1514, and an inductor 1531 for providing electromagnetic interference (EMI) filtering.

The smart switch 1502 includes a power supply 1520 that is coupled between the hot terminal H and a neutral terminal N, such that no current is drawn through the lighting load 1508 in order to charge the power supply 1520. The power supply 1520 generates a DC voltage for powering a controller 1518. The DC voltage V_(CC) is referenced to circuit common, i.e., the neutral terminal N. A user interface 1528 includes a toggle button for toggling the lighting load 1508 between on and off, and an LED for displaying the state of the lighting load.

The smart switch 1502 further comprises two sense circuits 1536, 1538, and a resistor 1560 coupled between the first and second switched hot terminals SH1, SH2. The sense circuits 1536, 1538 operate as zero-crossing detectors (to allow the controller 1518 to phase control the triacs 1510, 1512 appropriately) and as voltage detect circuits (to allow the controller to determine the state of the connected three-way switch 1504 and thus the state of the lighting load 1508. In response to determining the state of the three-way switch 1504, the controller 1508 may illuminate the LED of the user interface 1528, or transmit feedback information to other control devices via a communication circuit 1534. The controller 1518 is coupled to a memory 1532 for storage of the state of the triacs 1510, 1512 and the three-way switch 1504.

The first sense circuit 1536 comprises a resistor divider, which includes two resistors 1540, 1542 and is coupled between the switched hot terminal SH1 and circuit common, i.e., the neutral terminal N. The junction of the resistors 1540, 1542 is coupled to the base of an NPN bipolar junction transistor (BJT) 1544. The collector of the transistor 1544 is coupled to the DC voltage V_(CC) through a resistor 1546 (e.g., having a resistance of 15 kΩ) and is provided as an output to the controller 1518. The resistors 1540, 1542 preferably have resistances of 110 kΩ and 4.7 kΩ, respectively, such that when the switched hot voltage at the switched hot terminal SH1 is below a predetermined level, e.g., approximately 17 V, the output to the controller 1518 is pulled up to approximately the DC voltage V_(CC). When the dimmed hot voltage exceeds the predetermined level, the transistor 1544 begins to conduct, pulling the output to approximately circuit common.

The second sense circuit 1538 includes similar components as the first sense circuit 1536 and operates in the same manner. The second sense circuit 1538 comprises resistors 1550, 1552, 1556 and an NPN bipolar junction transistor 1554. Since the controller 1518 drives the triacs 1510, 1514 on a complementary basis and the sense circuits 1536, 1538 are referenced to the neutral terminal N, the controller 1518 is operable to receive the zero-crossing information of the AC power supply 1506 independent of the position of the three-way switch 1504.

The controller 1518 also uses the sense circuits 1536, 1538 to determine the state of the connected three-way switch 1504. When the controller 1518 is driving the second triac 1514, the second sense circuit 1538 is operatively coupled between the hot terminal H and the neutral terminal N at the beginning of each half cycle of the AC voltage source 1506. As shown in FIG. 15B, a second switched hot voltage V_(TRAVELER 2) is provided at the second switched hot terminal SH and a second zero-crossing signal V_(ZC2) is generated at the output of the second sense circuit 1538. The first sense circuit 1536 is coupled to the second switched hot terminal SH1 through the resistor 1560.

When the three-way switch 1504 is in position B, a first switched hot voltage V_(TRAVELER 1) is provided at the first switched hot terminal SH1 and is a scaled version of the second switched hot voltage V_(TRAVELER 2). A first zero-crossing signal V_(ZC1), having different shape than the second zero-crossing signal V_(ZC2), is generated at the output of the first sense circuit 1536 as shown in FIG. 15B. However, when the three-way switch 1504 is in position A, the first switch hot voltage V_(TRAVELER 1) has a magnitude of substantially zero volts (as shown in FIG. 15C) since the impedance of the lighting load 1508 (e.g., approximately 400Ω or less) is much smaller than the impedance of the first sense circuit 1536 (i.e., the sum of the resistances of the resistors 1540, 1542). As a result, the first zero-crossing signal V_(ZC1) also has a magnitude of substantially zero volts.

When the controller 1518 is driving the second triac 1514, the controller is operable to determine the state of the connected three-way switch 1504 in response to whether the first zero-crossing signal V_(ZC1) is being provided or not. Similarly, when the controller 1518 is driving the first triac 1510, the controller is operable to determine the state of the connected three-way switch 1504 in response to whether the second zero-crossing signal V_(ZCs) is being provided or not. In summary, the controller 1518 is operable to determine that the lighting load 1508 is on if both zero-crossing signals V_(ZC1), V_(ZC2) are being generated and to determine that the lighting load 1508 is off if only one of the two zero-crossing signals V_(ZC1), V_(ZC2) is being generated.

FIG. 15D is a simplified flowchart of a smart switch procedure 1570, which is executed by the controller 1518 periodically, e.g., once every half-cycle of the AC voltage source 1506. First, the controller 1518 checks to determine if the toggle button of the user interface 1528 is being pressed at step 1572. If the toggle button is being pressed at step 1574, the controller 1518 changes which triac 1510, 1514 is being driven in a complementary manner. In other words, if the controller 1518 is presently driving the first triac 1510 at step 1576, the controller begins to drive the second triac 1514 at step 1578. If the controller 1518 is not presently driving the first triac 1510 at step 1576, the controller begins to drive the first triac at step 1580.

Next, the controller 1518 checks the inputs from the first and second sense circuits 1536, 1538 (i.e., the first and second zero-crossing signals V_(ZC1), V_(ZC2)) at step 1582 in order to determine the state of the connected three-way switch 1504 and the state of the lighting load 1508. If the controller 1518 is receiving both of the zero-crossing signals V_(ZC1), V_(ZC2) at step 1584, the controller 1518 determines that the lighting load 1508 is on at step 1586 an the procedure 1570 exits. The controller 1518 is operable to then illuminate the LED of the user interface 1528 or to transmit feedback information via the communication circuit 1534. If controller 1518 is not receiving both of the zero-crossing signals V_(ZC1), V_(ZC2) at step 1584, but the controller is receiving only one of the two zero-crossing signals V_(ZC1), V_(ZC2) at step 1588, the controller determines that the lighting load 1508 is off at step 1590 and the procedure 1570 exits.

FIG. 16A is a simplified block diagram of a three-way system 1600 that includes a smart switch 1602 according to a sixth embodiment of the present invention. As with the smart switch 1502 of FIG. 15A, the smart switch 1602 includes two triacs 1510, 1514, which are controlled by a controller 1618 in a complementary manner. A first zero-crossing detector 1626 is coupled between the first switched hot terminal SH1 and the neutral terminal N, and a second zero-crossing detector 1627 is coupled between the second switched hot terminal SH2 and the neutral terminal N. The controller 1618 receives the zero-crossing signals representative of the zero-crossings of the AC voltage source 1506 from the first and second zero-crossing detectors 1626, 1627. The first and second zero-crossing detectors 1626, 1627 have similar structures as the first and second sense circuits 1526, 1528 of the smart dimmer 1502 of FIG. 15A.

The smart switch 1602 further comprises first and second gate drive circuits 1612, 1616 coupled in series between the gate and one of the main load terminals of each of the first and second triacs 1510, 1514, respectively. The first gate drive circuit 1612 includes a trigger circuit 1640, which is responsive to the controller 1618, and a current sense circuit 1642, which provides an active-low gate current (GC) control signal to the controller. The controller 1618 is operable to drive the first triac 1510 by controlling the trigger circuit 1640 to conduct the gate current through the gate of the first triac 1510 to thus render the first triac conductive at a predetermined time each half-cycle of the AC voltage source 1506. The GC control signal is generated by the current sense circuit 1642 and comprises a DC voltage representative of the magnitude of the gate current. The controller 1618 is operable to determine if the gate current is flowing through the gate of the first triac 1510 in response to the GC control signal. The gate of the first triac 1510 is coupled to the trigger circuit 1640 via a resistor 1646 and to the second of the main load terminals via a resistor 1648. The resistors 1646, 1648 preferably both have resistances of 220Ω.

The second gate drive circuit 1616 has a similar structure as the first gate drive circuit 1612 and comprises a trigger circuit 1650 and a current sense circuit 1652. The gate of the second triac 1514 is coupled to the trigger circuit 1650 via a resistor 1656 (e.g., 220Ω) and to the second of the main load terminals via a resistor 1658 (e.g., 220Ω).

The smart switch 1602 further comprises a line voltage detect (LVD) circuit 1660, which is coupled between the hot terminal H and the neutral terminal N. The line voltage detect circuit 1660 provides an active-low LVD control signal to the controller 1618. The controller 1618 is operable to determine whether the AC line voltage is present at the hot terminal H in response to the line voltage detect circuit 1660. The line voltage detect circuit 1660 allows the controller 1618 to determine if the lighting load 1508 is on when the dimmer 1602 is coupled to the load side of the system 1600 (as shown in FIG. 16C). Accordingly, the controller 1618 is operable to determine the state of the three-way switch 1504 and the lighting load 1508 in response to the current sense circuits 1642, 1652 and the line voltage detect circuit 1660.

FIG. 16B is a simplified schematic diagram showing the current sense circuits 1642, 1652 and the line voltage detect circuit 1660 in greater detail. The line voltage detect circuit 1660 preferably operates as a zero-crossing detector and has a similar structure as the first and second sense circuits 1526, 1528 of the smart dimmer 1502 of FIG. 15A. The resistors 1662, 1664, 1668 have resistances of 110 kΩ, 1.0 kΩ, and 15 kΩ, respectively. When the line voltage detect circuit 1660 does not provide a zero-crossing signal to the controller 1618, the controller is operable to determine that the lighting load 1508 is off.

The trigger circuit 1640 of the first gate drive circuit 1612 comprises an opto-triac, having an input (i.e., a photo-diode) coupled between the controller 1618 and circuit common, and an output (i.e., a photo-triac) coupled in series with the gate of the first triac 1510. The current sense circuit 1642 comprises an opto-coupler having an input (i.e., two photo-diodes) coupled in series with the gate of the first triac 1510 and the photo-triac of the opto-triac. The opto-coupler also includes an output (i.e., a photo-transistor), coupled between the controller 1618 and circuit common. When the gate current is not flowing through either of the photo-diodes of the opto-coupler, the photo-transistor is non-conductive and the output provided to the controller 1618 is pulled up to substantially the DC voltage V_(CC) through a resistor 1644. However, when the gate current is flowing, the photo-transistor pulls the output to the controller 1618 to substantially circuit common (i.e., approximately zero volts). The second gate drive circuit 1616 has a similar structure as the first gate drive circuit 1612. The first and second gate drive circuits 1612, 1616 are characterized such that the current sense circuits 1642, 1652 signal to the controller 1618 that the gate current is flowing (i.e., pull the GC control signal low) when the gate current has a magnitude of approximately 1 mA or greater.

FIG. 17A is a simplified diagram showing waveforms of the operation of the smart switch 1602 when the smart switch is coupled to the line side of the system 1600 (as shown in FIG. 16A), the controller 1618 is driving the first triac 1510, and the three-way switch 1504 is in position A, such that the lighting load 1508 is on. Since the AC line voltage signal is present at the hot terminal H, the line voltage detect circuit 1660 drives the LVD control signal low around the peak of the AC line voltage signaling to the controller 1618 that the AC line voltage is present. The controller 1618 cannot determine the state of the lighting load 1508 from the LVD control signal, but must check one of the GC control signals.

The gate current for the first triac 1510 flows through the AC voltage source 1506, the first triac 1510, the trigger circuit 1640, the current sense circuit 1642, and the first zero-crossing detector 1626 to the neutral terminal N. Immediately after each zero-crossing of the AC line voltage, the controller 1618 drives the trigger circuit 1640 to fire the first triac 1510. Accordingly, the gate current flows into the gate of the first triac for a period of time until the load current through the main terminals of the triac exceeds a latching current rating and the triac becomes conductive. The voltage across the triac 1510 then drops to a substantially low voltage (e.g., approximately 1 V) and the gate current stops flowing. Therefore, the gate current exists as a pulse of current when the triac successfully fires. The GC control signal generated by the current sense circuit 1642 is low (i.e., at substantially zero volts) when the gate current is following, and is high (i.e., at substantially the DC voltage V_(CC)) when the gate current is flowing as shown in FIG. 17A.

FIG. 17B is a simplified diagram showing waveforms of the operation of the smart switch 1602 when the smart switch is coupled to the line side of the system 1600 and the controller 1618 is driving the first triac 1510, but the three-way switch 1504 is in position B, such that the lighting load 1508 is off. In this case, the first triac 1510 does not become conductive since the current through the main terminals of the triac cannot exceed the latching current rating. The impedance of the zero-crossing detector 1626 (e.g., approximately 60 kΩ) sets the magnitude of the gate current to a voltage below the latching current rating of the first triac 1510. Since the first triac 1510 does not become conductive, the gate current continues to flow and has a magnitude greater than substantially zero amps (i.e., approximately 1 mA or greater as determined by the impedance of the zero-crossing detector 1626) for substantially the length of each half-cycle. Accordingly, the GC control signal is pulled low to circuit common (i.e., to approximately zero volts) for substantially the entire length of each half-cycle, signaling that the first triac 1512 is not conducting the load current.

When the smart switch 1602 is coupled to the line-side of the system 1600 (as shown in FIG. 16A), the controller 1618 is operable to determine the state of the lighting load 1508 in response to the current sense circuits 1642, 1652. Specifically, the controller 1618 monitors the output of the current sense circuit 1642, 1652 that is coupled in series with the gate of the triac that is presently being driven during a sampling window near the peak of the AC line voltage. If the gate current is not flowing (i.e., the gate current has a magnitude of substantially zero amps), the controller 1618 determines that the triac is conductive and the lighting load 1508 is on. If the gate current is flowing (i.e., the gate current has a magnitude greater than substantially zero amps), the controller 1618 determines that the triac is not conducting current to the load and the lighting load 1508 is off.

Preferably, the sampling window is a period of time having a length T_(WINDOW) (e.g., approximately 1.5 msec) centered around a time t_(PEAK) corresponding to the peak of the AC line voltage as shown in FIGS. 17A and 17B. The sampling window is centered around the peak of the AC line voltage to ensure that the controller 1618 does not sample the GC control signal around the zero-crossings. Near the zero-crossings, the opto-triacs of the trigger circuits 1640, 1650 of the first and second gate drive circuits 1612, 1614 may not have sufficient current flowing through the photo-triacs to remain conductive. This may cause the opto-couplers of the current sense circuits 1642, 1652 to allow the GC control signal to be high (i.e., the same condition as when one of the triacs 1510, 1514 has become conductive and the gate current has stopped flowing).

When the smart switch 1602 is coupled to the load-side of the system 1600 (as shown in FIG. 16C), the controller 1618 cannot determine the state of the lighting load 1508 solely from the current sense circuits 1642, 1652. The controller 1618 must also use the line voltage detect circuit 1660 determine the state of the lighting load 1508. If the controller 1618 is not driving the triac 1510, 1514 that is in series with the present position of the three-way switch 1504, the AC line voltage is not present across the line voltage detect circuit 1660. The line voltage detect circuit 1660 provides an appropriate control signal to the controller 1618, which concludes that the lighting load 1508 is off. If the AC line voltage is coupled across the line voltage detect circuit 1660 and the gate current is flowing through the gate of the triac that the controller 1618 is driving, the controller determines that the lighting load 1508 is on.

FIG. 18A is a simplified flowchart of a button procedure 1800 executed by the controller 1618 periodically, e.g., once every 10 msec, to determine if the toggle button of the user interface 1528 is being pressed. The controller 1618 uses a variable BUT_COUNT to keep track of how long the toggle button has been pressed. Specifically, the variable BUT_COUNT keeps track of how many consecutive times that the button procedure 1800 is executed while the toggle button is pressed.

Referring to FIG. 18A, the controller 1618 first checks the input provided from the user interface 1528 at step 1810 to determine if the toggle button of the user interface is being pressed. If the toggle button is not being pressed at step 1812, the controller 1618 clears the variable BUT_COUNT at step 1814. However, if the toggle button is being pressed at step 1812, the controller increments the variable BUT_COUNT at step 1816. If the variable BUT_COUNT is not equal to a maximum value, e.g., two (2), at step 1818, the button procedure 1800 simply exits.

If the variable BUT_COUNT is equal to two at step 1818 (i.e., the toggle button has been pressed during two consecutive executions of the button procedure 1800), a determination is made at step 1820 as to whether the controller 1618 is presently controlling the first triac 1510. If so, the controller 1618 begins to control the second triac 1514 each half-cycle at step 1822 (as will be described in greater detail below). If the controller 1618 is not controlling the first triac 1510 at step 1820, the controller begins to control the second triac 1514 each half-cycle at step 1824. Finally, the variable BUT_COUNT is cleared at step 1826 and the button procedure 1800 exits.

FIGS. 18B and 18C are simplified flowcharts of a zero-crossing procedure 1830 executed by the controller 1618 periodically in response to receiving an indication of a zero-crossing from either one of the zero-crossing detectors 1626, 1627, i.e., once every half cycle of the AC voltage source 1506. After the zero-crossing at step 1832 each half-cycle, the controller 1618 first renders one of the first and second triacs 1510, 1514 conductive substantially immediately following the zero-crossing (i.e., as soon as the magnitude of the AC line voltage is high enough that the triacs 1510, 1514 may be fired). Specifically, if the controller 1618 is controlling the first triac 1510 at step 1834, the controller drives the first triac via the first gate drive circuit 1612 at step 1836. Alternatively, if the controller 1618 is controlling the second triac 1514 at step 1834, the controller drives the second triac via the second gate drive circuit 1616 at step 1838. If the controller 1618 determines that the present half-cycle is the negative half-cycle at step 1840, the controller waits for the end of the half-cycle at step 1854, after which the controller stops driving the appropriate triac 1510, 1514 at step 1856.

If the present half-cycle is the positive half-cycle at step 1840, the controller 1618 determines at step 1842 whether the AC line voltage has entered the sampling window, i.e., the period of time of 1.5 msec surrounding the peak of the AC line voltage as shown in FIGS. 17A and 17B. The controller 1618 waits at step 1842 until the AC line voltage is in the sampling window, at which time, the controller begins to periodically sample the LVD control signal and the GC control signal to determines if the AC line voltage is present at the hot terminal H and the gate current is flowing through the gate of one of the first and second triacs 1510, 1514, respectively. Preferably, the controller 1618 samples the control signals approximately every 250 μsec, such that the controller obtains approximately six (6) samples of each of the control signals during the sampling window. The controller 1618 uses two variables LVD_COUNT and GC_COUNT to keep track of how many of the six samples of the LVD control signal is high and the GC_COUNT control signal is low during the sampling window, respectively.

Referring to FIG. 18C, the controller 1618 checks the LVD control signal from the line voltage detect circuit 1660 at step 1844 to determine whether the AC line voltage is present at the hot terminal H. If the AC line voltage is not detected at step 1846, the controller 1618 increments the variable LVD_COUNT at step 1848. If the variable LVD_COUNT is equal to a maximum value, e.g., two (2), at step 1850 (i.e., two of the six samples of the LVD control signal are high during the sampling window), the controller 1618 executes an OFF routine 1890, which will be explained in greater detail below with reference to FIG. 18E. The OFF routine 1890 provides some digital filtering to ensure that the state of the lighting load 1508 as determined by the controller 1618 does not change too often. The zero-crossing procedure 1830 must execute the OFF routine 1890 during a predetermined number of consecutive half-cycles, e.g., approximately twelve (12) consecutive half-cycles, before the controller 1618 determines that the lighting load 1508 is off. After executing the OFF routine 1890, the controller 1618 clears the variables LVD_COUNT and GC_COUNT at step 1852. At the end of the half-cycle at step 1854, the controller 1618 stops driving the appropriate triac 1510, 1514 at step 1856 and the procedure 1830 exits.

If the AC line voltage is detected at step 1846 or if the variable LVD_COUNT is not equal to two at step 1850, the controller 1618 determines whether the gate current is flowing through the gate of one of the first and second triacs 1510, 1514. Specifically, if the controller 1618 is presently driving the first triac 1510 at step 1858, the controller monitors the output of the first current sense circuit 1642 of the first gate drive circuit 1612 at step 1860 to determine if the gate current is presently flowing through the gate of the first triac 1510. If the controller 1618 is presently driving the second triac 1514 at step 1858, the controller monitors the output of the second current sense circuit 1652 of the second gate drive circuit 1616 at step 1862 to determine if the gate current is presently flowing through the gate of the second triac 1514. If the gate current is not flowing through the gate of the first triac 1510 or the gate of the second triac 1514 during the sampling window at step 1864, the controller 1618 increments the variable GC_COUNT at step 1866. If the variable GC_COUNT is equal to a maximum number, e.g., two (2), at step 1868, the controller executes an ON routine 1880, which will be described in greater detail below with reference to FIG. 18D. Similar to the OFF routine 1890, the ON routine 1880 guarantees that the state of the lighting load 1508 as determined by the controller 1618 does not change too often by ensuring that the controller 1618 detects that gate current is not flowing through the gate of the controlled triac for a predetermined number of consecutive half-cycles, e.g., approximately twelve (12) consecutive half-cycles, before determining that the lighting load 1508 is on. After executing the ON routine 1880, the controller 1618 clears the variables LVD_COUNT and GC_COUNT at step 1852 and stops driving the appropriate triac 1510, 1514 at the end of the half-cycle at step 1856, before the procedure 1830 exits.

If the gate current is flowing through either of the gates of the triacs 1510, 1514 during the sampling window at step 1864 or if the variable GC_COUNT is not equal to two at step 1868, the controller 1618 determines whether the AC line voltage has reached the end of the sampling window at step 1870. If not, the controller 1618 waits at step 1872 and then samples the LVD control signal and the GC control signal again, such that the control signals are sampled approximately every 250 μsec. If the AC line voltage has reached the end of the sampling window at step 1870, the controller 1618 executes the OFF routine 1890 and clears the variables LVD_COUNT and GC_COUNT at step 1852, before ceasing to drive the appropriate triac 1510, 1514 at step 1856. Finally, the procedure 1850 exits.

FIGS. 18D and 18E are simplified flowcharts of the ON routine 1880 and the OFF routine 1890, respectively, which are both called from the zero-crossing procedure 1830. The controller 1618 uses two variables ON_COUNT and OFF_COUNT to keep track of how many consecutive half-cycles that the zero-crossing procedure 1830 has executed the ON routine 1880 and the OFF routine 1890, respectively.

During the ON routine 1880, the variable OFF_COUNT is cleared (i.e., set to zero) at step 1882 and the variable ON_COUNT is incremented by one at step 1884. If the variable ON_COUNT is less than eleven (11) at step 1886, the ON routine 1880 simply exits. If the variable ON_COUNT is greater than eleven, i.e., is twelve (12) or greater, at step 1886, the controller 1618 determines that the lighting load 1508 is on at step 1888 and the ON routine 1880 exits. In contrast, during the OFF routine 1890, the variable ON_COUNT is cleared (i.e., set to zero) at step 1892 and the variable OFF_COUNT is incremented by one at step 1894. When the variable OFF_COUNT is greater than eleven at step 1896, the controller 1618 determines that the lighting load 1508 is off at step 1898.

Preferably, the variables LVD_COUNT, GC_COUNT, ON_COUNT, OFF_COUNT used by the controller 1618 during the zero-crossing procedure 1830 are initialized to zero during a start-up procedure of the controller 1618.

Upon determining the state of the lighting load 1508 using the zero-crossing procedure 1830, the controller 1618 is able to control the visual display of the user interface 1528 to provide feedback of the state of the lighting load 1508 and to report the state of the lighting load 1508 via the communication circuit 1534.

FIG. 19 is a simplified block diagram of a three-way system 1900 that includes a smart dimmer 1902 according to a seventh embodiment of the present invention. The smart dimmer 1902 includes similar functional blocks as the smart switch 1602 of FIG. 16A. However, the smart dimmer 1902 does not require a neutral connection. Further, the smart dimmer 1902 is operable to control the amount of power delivered to the lighting load 1508 to thus control the intensity of the lighting load. A controller 1918 controls the triacs 1510, 1514 on a complementary basis, i.e., in a similar manner as the smart dimmer 502 of FIG. 5A, using forward phase control dimming. A power supply 1920 and a zero-crossing detector 1926 are coupled across the first and second triacs 1510, 1514 via two diodes 1922, 1924, respectively.

As with the smart switch 1602 of FIG. 16A, the controller 1918 is operable to control the trigger circuit 1640, 1650 of the gate drive circuits 1612, 1616 to fire the triacs 1510, 1512, respectively. The controller 1918 is also operable to determine if the gate current is flowing in response to the current sense circuits 1642, 1652 of the gate drive circuit 1612, 1616, respectively. A resistor 1960 is coupled between the dimmed hot terminals DH1, DH2 to allow the gate currents to flow through the gate drive circuits 1612, 1616 regardless of the position of the connected three-way switch 1504.

FIG. 20A is a simplified diagram showing waveforms of the operation of the smart dimmer 1902 when the smart dimmer is coupled to the line side of the system 1900, the controller 1918 is driving the first triac 1510, and the three-way switch 1504 is in position A, such that the lighting load 1508 is on. The gate current for the first triac 1510 flows through the AC voltage source 1506, the first triac 1510, the trigger circuit 1640, the current sense circuit 1642, the three-way switch 1504, and the lighting load 1508. The controller 1918 renders the triac 1510 conductive at a firing time t_(FIRE) each half-cycle depending upon the desired lighting level of the light load 1508. After the first triac 1510 is fired, the gate current flows into the gate of the first triac for a period of time until the load current through the main terminals of the first triac exceeds a latching current rating and becomes conductive. The GC control signal generated by the current sense circuit 1642 is pulled low to circuit common when the gate current is flowing as shown in FIG. 20A.

FIG. 20B is a simplified diagram showing waveforms of the operation of the smart dimmer 1902 when the smart dimmer is coupled to the line side of the system 1900 and the controller 1918 is driving the first triac 1510, but the three-way switch 1504 is in position B, such that the lighting load 1508 is off. Since the three-way switch 1504 is in position B, the gate current for the first triac 1510 flows through the AC voltage source 1506, the first triac 1510, the trigger circuit 1640, the current sense circuit 1642, the resistor 1960, the three-way switch 1504, and the lighting load 1508. The resistor 1960 preferably has a resistance of 110 kΩ, such that the magnitude of the gate current is prevented from exceeding the latching current rating of the triac 1510. Since the first triac 1510 does not become conductive, the gate current continues to flow and has a magnitude greater than zero (i.e., as determined by the impedance of the zero-crossing detector 1626) for substantially the length of each half-cycle. Accordingly, the GC control signal is pulled low to circuit common for the rest of the half-cycle after the controller 1918 attempts to drive the first triac 1510, signaling that the first triac is not conducting the load current. The resistance of the resistor 1960 is chosen such that the gate current is greater than approximately 1 mA and the current sense circuits 1642, 1652 pull the GC control signal low when the gate current is flowing.

The controller 1918 is operable to determine the state of the lighting load 1508 in response to the current sense circuits 1642, 1652 of the gate drive circuits 1512, 1516, respectively. After rendering one of the triacs 1510, 1512 conductive, the controller 1618 checks the GC control signal provided by the current sense circuit 1642, 1652 of the controlled triac. Preferably, the controller 1918 samples the GC control signal at a time t_(SAMPLE) after the controller begins driving the triac via the appropriate trigger circuit 1640, 1650 as shown in FIGS. 20A and 20B. If the gate current is not flowing (i.e., the gate current has a magnitude of substantially zero volts and the GC control signal is high) at the sampling time t_(SAMPLE), the controller 1918 determines that the triac is conducting the load current and the lighting load 1508 is on. If the gate current is flowing (i.e., the gate current has a magnitude greater than substantially zero volts and the GC control signal is low) at the sampling time t_(SAMPLE), the controller 1918 determines that the controlled triac is not conducting the load current and the lighting load 1508 is off.

FIG. 21 is a simplified flowchart of a zero-crossing procedure 2100 executed by the controller 1918 periodically in response to receiving an indication of a zero-crossing from the zero-crossing detector 1926, i.e., once every half cycle of the AC voltage source 1506. The controller 1918 also executes the button procedure 1800 of FIG. 18A periodically, e.g., approximately once every 10 msec, to determine which of the triacs 1510, 1514 to control. Referring to FIG. 21, when the controller 1918 receives an indication of a zero-crossing at step 2110 each half-cycle, the controller renders one of the first and second triacs 1510, 1514 conductive at the appropriate firing time t_(FIRE) after the zero-crossing. Specifically, if the controller 1918 is controlling the first triac 1510 at step 2112, the controller drives the first triac at the firing time t_(FIRE) via the first gate drive circuit 1612 at step 2114. If the controller 1918 is controlling the second triac 1514 at step 2112, the controller drives the second triac at the firing time t_(FIRE) via the second gate drive circuit 1616 at step 2116. The controller 1918 continues to drive the appropriate triac 1510, 1514 for a period of time, e.g., 200 μsec, at step 2118.

After the period of time expires at step 2118, the controller 1918 checks one of the GC control signals from the current sense circuits 1642, 1652 to determine the state of the lighting load 1508. If the controller 1918 is controlling the first triac 1510 at step 2120, the controller samples the GC control signal of the current sense circuit 1642 of the first gate drive circuit 1612 at step 2122. Otherwise, the controller 1918 samples the GC control signal of the current sense circuit 1652 of the second gate drive circuit 1616 at step 2124. If the sample of the appropriate GC control signal shows at step 2126 that there is gate current flowing at the sampling time t_(SAMPLE), the controller 1918 executes the OFF routine 1880 of FIG. 18E and eventually determines that the lighting load 1508 is off if there is gate current flowing for twelve consecutive half-cycles. If the gate current is not flowing at step 2126, the controller 1918 executes the ON routine 1880 of FIG. 18D and eventually determines that the lighting load 1508 is on if there is not gate current flowing for twelve consecutive half-cycles. Next, the controller 1918 stops driving the appropriate triac 1510, 1514 at step 2128 and the procedure 2100 exits.

The smart switches 1502, 1602 could alternatively operate as smart dimmers to provide phase-control dimmed-hot signals to the connected lighting load 1508 to control the intensity of the lighting load.

The smart dimmers 502, 602, 702, 802, 1902 and smart switches 1502, 1602 are useful in three-way and four-way applications without the requirement of replacing the standard switches already installed in the other switching location(s). Unlike applications described above in the prior art, all other switches at other switching locations in the same three-way or four-way circuit do not have to be replaced with an accessory dimmer. Accordingly, the present invention has a reduced cost. Only one smart three-way or four-way dimmer or switch need be purchased and the existing switches in the three-way or four-way switching circuit remain fully operational. By installing a single smart dimmer 502, 602, 702, 802, 1902 or smart switch 1502, 1602, less time is required for installation, thereby reducing installation costs. Also, there is less chance of errors in installation (e.g., mistakes in wiring), further reducing installation costs and the likelihood of damaging and replacing units.

Thus, the smart dimmers 502, 602, 702, 802, 1902 and smart switches 1502, 1602 are configurable as three-way or four-way (or multi-way) switches that improve upon prior art smart dimmers and smart switches. In accordance with the present invention, the dimmers are relatively inexpensive to manufacture, and are easier to install in existing electrical systems than prior art smart dimmers providing three-way and four-way switching functionality. For example, users are not required to replace other existing three-way switches with accessory dimmers. Moreover, modifications to wiring of the other existing three-way switches is avoided.

Furthermore, the various examples of three-way dimmers 502, 602, and 702 illustrated herein are each shown as connected directly to the line-side of the lighting control systems. One of ordinary skill in the art will recognize that, in the alternative, the dimmers 502, 602, and 702 could be wired on the load-side of the systems.

Although the words “device” and “unit” have been used to describe the elements of the lighting control systems of the present invention, it should be noted that each “device” and “unit” described herein need not be fully contained in a single enclosure or structure. For example, the dimmer 502 of FIG. 5 may comprise a plurality of buttons in a wall-mounted enclosure and a controller that is included in a separate location. Also, one “device” may be contained in another “device”. For example, the semiconductor switch (i.e., the controllably conductive device) is a part of the dimmer of the present invention.

The present application is also related to commonly-assigned co-pending U.S. patent application Ser. No. 11/536,450, filed Aug. 9, 2007, entitled LOAD CONTROL DEVICE HAVING A GATE CURRENT SENSING CIRCUIT, the entire disclosure of which is hereby incorporated by reference.

Although the present invention has been described in relation to particular embodiments thereof, many other variations and modifications and other uses will become apparent to those skilled in the art. Therefore, the present invention should not be limited by the specific disclosure herein. 

1. A load control device adapted to be coupled to a circuit including an AC power source, a load, and a single-pole double-throw (SPDT) three-way switch, the AC power source generating an AC line voltage for powering the load, the SPDT three-way switch comprising a first fixed contact, a second fixed contact, and a moveable contact adapted to be coupled to either the power source or the load, the SPDT three-way switch having a first state in which the moveable contact is contacting the first fixed contact and a second state in which the moveable contact is contacting the second fixed contact, the load control device comprising: a first load terminal adapted to be coupled to one of the power source or the load to which the SPDT three-way switch is not coupled; a second load terminal adapted to be coupled to the first fixed contact of the SPDT three-way switch; a third load terminal adapted to be coupled to the second fixed contact of the SPDT three-way switch; a first controllably conductive device having a conductive state and a non-conductive state, the first controllably conductive device electrically coupled between the first load terminal and the second load terminal such that when the first controllably conductive device is in the conductive state and the load control device is coupled to the circuit, the first controllably conductive device is operable to allow a load current to flow between the first load terminal and the second load terminal for at least a portion of each half-cycle of the AC line voltage, the first controllably conductive device having a first control input and operable to enter the conductive state in response to a first gate current conducted through the first control input; a second controllably conductive device having a conductive state and a non-conductive state, the second controllably conductive device electrically coupled between the first load terminal and the third load terminal such that when the second controllably conductive device is in the conductive state and the load control device is coupled to the circuit, the second controllably conductive device is operable to allow the load current to flow between the first load terminal and the third load terminal for at least a portion of each half-cycle of the AC line voltage, the second controllably conductive device having a second control input and operable to enter the conductive state in response to a second gate current conducted through the second control input; and a controller operable to control the first and second controllably conductive devices to control the load between an on state and an off state, the controller operable to drive the first controllably conductive device to change the first controllably conductive device from the non-conductive state to the conductive state each half-cycle of the AC line voltage, the controller operable to determine, in response to the magnitude of the first gate current through the first control input of the first controllably conductive device, whether the first controllably conductive device is presently conducting current to the load.
 2. The load control device of claim 1, wherein the controller is further operable to drive the second controllably conductive device, such that the second controllably conductive device is operable to change from the non-conductive state to the conductive state, the controller operable to determine if the second controllably conductive device is presently conducting current to the load in response to the magnitude of the second gate current through the second control input of the second controllably conductive device.
 3. The load control device of claim 2, further comprising: a first sense circuit having an input operatively coupled to the control input of the first controllably conductive device and an output operatively coupled to the controller, the first sense circuit operable to provide a first control signal representative of the magnitude of the first gate current to the controller; and a second sense circuit having an input operatively coupled to the control input of the second controllably conductive device and an output operatively coupled to the controller, the second sense circuit operable to provide a second control signal representative of the magnitude of the second gate current to the controller.
 4. The load control device of claim 3, wherein the controller is operable to determine that the load is in the on state if one of the first and second gate currents has a magnitude of substantially zero amps.
 5. The load control device of claim 4, wherein the controller is operable to determine that the load is in the off state if one of the first and second gate currents has a magnitude greater than substantially zero amps.
 6. The load control device of claim 5, wherein the controller is operable to determine that the load is in the off state if the first gate current has a magnitude greater than substantially zero amps when the controller is driving the first controllably conductive device, and to determine that the load is in the off state if the second gate current has a magnitude greater than substantially zero amps when the controller is driving the second controllably conductive device.
 7. The load control device of claim 6, wherein the controller is operable to determine that the load is in the off state if the first gate current has a magnitude greater than approximately one milliamp when the controller is driving the first controllably conductive device, and to determine that the load is in the off state if the second gate current has a magnitude greater than approximately one milliamp when the controller is driving the second controllably conductive device.
 8. The load control device of claim 4, wherein the controller is operable to determine that the load is in the on state if the first gate current has a magnitude of substantially zero amps when the controller is driving the first controllably conductive device, and to determine that the load is in the on state if the second gate current has a magnitude of substantially zero amps when the controller is driving the second controllably conductive device.
 9. The load control device of claim 3, further comprising: a line voltage detect circuit operatively coupled to the first terminal to detect the presence of the AC line voltage at the first terminal.
 10. The load control device of claim 9, wherein the controller is operable to determine that the load is in the off state if the AC line voltage is not present at the first terminal.
 11. The load control device of claim 10, wherein the controller is operable to determine that the load is in the on state if one of the first and second gate currents has a magnitude of substantially zero amps.
 12. The load control device of claim 9, further comprising: a neutral terminal; wherein the line voltage detect circuit is coupled between the first terminal and the neutral terminal.
 13. The load control device of claim 3, wherein the first and second sense circuits comprise first and second current sense circuits.
 14. The load control device of claim 13, further comprising: a first trigger circuit coupled in series electrical connection with the first control input of the first controllably conductive device and the input of the first sense circuit; and a second trigger circuit coupled in series electrical connection with the second control input of the second controllably conductive device and the input of the second sense circuit; wherein the first and second trigger circuits are responsive to the controller.
 15. The load control device of claim 14, wherein the first and second trigger circuits comprise opto-triacs.
 16. The load control device of claim 13, wherein the first and second current sense circuits comprise opto-couplers.
 17. The load control device of claim 3, wherein the controller is operable to determine that the load is in the on state if the first gate current is not flowing near the peak of the AC line voltage when the controller is driving the first controllably conductive device, and to determine that the load is in the on state if the second gate current is not flowing near the peak of the AC line voltage when the controller is driving the first controllably conductive device.
 18. The load control device of claim 17, wherein the controller is operable to determine that the load is in the off state if the first gate current is flowing near the peak of the AC line voltage when the controller is driving the first controllably conductive device, and to determine that the load is in the off state if the second gate current is flowing near the peak of the AC line voltage when the controller is driving the second controllably conductive device.
 19. The load control device of claim 3, wherein the controller is operable to drive the first controllably conductive device at a predetermined time each half-cycle, and to monitor the first control signal from the first sense circuit after a predetermined amount of time has expired since the first controllably conductive device was driven by the controller.
 20. The load control device of claim 3, wherein the controller is operable to drive the first controllably conductive device at substantially the beginning of a half-cycle, and to monitor the first control signal from the first sense circuit during the half-cycle near a time corresponding to a peak voltage of the AC line voltage.
 21. The load control device of claim 2, further comprising: a neutral terminal; wherein gate current is conducted through the neutral terminal.
 22. The load control device of claim 21, further comprising: a first zero-crossing detector coupled to between the second terminal and the neutral terminal; and a second zero-crossing detector coupled to between the third terminal and the neutral terminal; wherein the first gate current is conducted through the first zero-crossing detector to the neutral terminal, and the second gate current is conducted through the second zero-crossing detector to the neutral terminal.
 23. The load control device of claim 21, further comprising: a power supply coupled between the first terminal and the neutral terminal, the power supply operable to provide power to the controller.
 24. The load control device of claim 2, wherein the first and second controllably conductive devices comprise bidirectional semiconductor switches.
 25. The load control device of claim 24, wherein the bidirectional semiconductor switches comprise triacs.
 26. The load control device of claim 2, further comprising: a communication circuit adapted to transmit a message including feedback information representative of the states of the first and second controllably conductive devices and the outputs of the first and second sensing devices.
 27. The load control device of claim 2, further comprising: a visual display for providing feedback to a user of the load control device.
 28. The load control device of claim 2, wherein the controller is operable to drive the first and second controllably conductive devices a complementary basis, such that when the first controllably conductive device is conductive, the second controllably conductive device is non-conductive, and when the second controllably conductive device is conductive, the first controllably conductive device is non-conductive.
 29. A method for controlling a load in a circuit comprising an AC power source, the load, a load control device, and a single-pole double-throw three-way switch, the three-way switch comprising a first fixed contact, a second fixed contact, and a movable contact adapted to be coupled to either the power source or the load, the three-way switch having a first state in which the movable contact is contacting the first fixed contact and a second state in which the movable contact is contacting the second fixed contact, the method comprising the steps of: providing a first load terminal on the load control device, the first load terminal adapted to be coupled to either the power source or the load to which the three-way switch is not coupled; providing a second load terminal on the load control device, the second load terminal adapted to be coupled to the first fixed contact of the three-way switch; providing a third load terminal on the load control device, the third load terminal adapted to be coupled to the second fixed contact of the three-way switch; electrically coupling a first controllably conductive device between the first load terminal and the second load terminal, the first controllably conductive device having a conductive state and a non-conductive, the first controllably conductive device arranged such that when the first controllably conductive device is in the conductive state, the first controllably conductive device is operable to allow a load current to flow between the first load terminal and the second load terminal for at least a portion of each half-cycle of the AC power source, the first controllably conductive device having a first control input; conducting a first gate current through the first control input to cause the first controllably conductive device to enter the conductive state; electrically coupling a second controllably conductive device between the first load terminal and the third load terminal, the second controllably conductive device having a conductive state and a non-conductive state, the second controllably conductive device arranged such that when the second controllably conductive device is in the conductive state, the second controllably conductive device is operable to allow the load current is operable to flow between the first load terminal and the third load terminal for at least a portion of each half-cycle of the AC power source, the second controllably conductive device having a second control input; conducting a second gate current through the second control input to cause the second controllably conductive device to enter the conductive state; monitoring the first and second gate currents; and determining, in response to the step of monitoring the first and second gate currents, whether the respective controllably conductive device is presently conducting the current to the load.
 30. The method of claim 29, wherein the step of monitoring further comprises monitoring the magnitudes of the first and second gate currents.
 31. The method of claim 30, further comprising the steps of: determining that the load is in the on state if the gate current presently has a magnitude of substantially zero amps.
 32. The method of claim 31, further comprising the steps of: determining that the load is in the off state if the gate current presently has a magnitude greater than substantially zero amps.
 33. The method of claim 29, further comprising the steps of: detecting the presence of a line voltage at the first terminal; and determining that the load is in the off state in response to the step of detecting the presence of line voltage.
 34. The method of claim 33, further comprising the steps of: determining that the load is in the on state if the gate current presently has a magnitude of substantially zero amps.
 35. The method of claim 29, wherein the step of conducting a first gate current comprises driving the first controllably conductive device at a predetermined time during a half-cycle, and the step of monitoring comprises monitoring the first control signal from the first sense circuit after a predetermined amount of time has expired since the step of driving the first controllably conductive device.
 36. The method of claim 29, wherein the step of conducting a first gate current comprises driving the first controllably conductive device at substantially the beginning of a half-cycle, and the step of monitoring comprises monitoring the first control signal from the first sense circuit during the half-cycle near a time corresponding to a peak voltage of the AC line voltage.
 37. The method of claim 29, further comprising the step of: transmitting a message including feedback information representative of the states of the first and second controllably conductive devices, the sensed first electrical characteristic, and the sensed second electrical characteristic.
 38. The method of claim 29, further comprising the step of: providing feedback to a user of the dimmer switch via a visual display.
 39. A load control system for controlling the amount of power delivered to an electrical load from an AC power source generating an AC line voltage, the load control system comprising: a single-pole double-throw (SPDT) three-way switch comprising a first fixed contact, a second fixed contact, and a movable contact adapted to be coupled to either the power source or the load, the SPDT three-way switch having a first state in which the movable contact is contacting the first fixed contact and a second state in which the movable contact is contacting the second fixed contact; and a load control device comprising: a first load terminal adapted to be coupled to either the power source or the load to which the SPDT three-way switch is not coupled to; a second load terminal coupled to the first fixed contact of the SPDT three-way switch; a third load terminal coupled to the second fixed contact of the SPDT three-way switch; a first controllably conductive device having a conductive state and a non-conductive state, the first controllably conductive device having a first control input and operable to enter the conductive state in response to a first gate current conducted through the first control input; a second controllably conductive device having a conductive state and a non-conductive state, the second controllably conductive device having a second control input and operable to enter the conductive state in response to a second gate current conducted through the second control input; and a controller operable to control the first and second controllably conductive devices, the controller operable to determine if the first controllably conductive device is presently conducting current to the load in response to the magnitude of the first gate current through the first control input of the first controllably conductive device; wherein when the SPDT three-way switch is in the first state, the controller is operable to control the first controllably conductive device such that a load current is operable to flow through the second load terminal when the first controllably conductive device is in the conductive state, and when the SPDT three-way switch is in the second state, the controller is operable to control the first controllably conductive device such that the load current is operable to flow through the third load terminal when the controllably conductive device is in the conductive state; and wherein the controller is operable to determine, in response to the magnitude of the first gate current through the first control input of the first controllably conductive device, whether the first controllably conductive device is presently conducting current to the load, the controller further operable to determine, in response to the magnitude of the second gate current through the second control input of the second controllably conductive device, whether the second controllably conductive device is presently conducting current to the load. 